Added MemberNotNullWhen in IApiResponse

[AlbertoMonteiro]

What kind of change does this PR introduce?
Better experience in development when using

What is the current behavior?

N/A

What is the new behavior?

It's just change the developer experience, avoiding using ! operator when is not required.

What might this PR break?

Nothing

Please check if the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

Other information:

With that change, if I am in the .NET 5 or higher after the if statement, compiler will know that response.Error is not null and I dont need to use response.Error!

var response = api.GetSomething();
if (!response.IsSuccessStatusCode)
{
    //....
}

_logger.LogError(response.Error, "Message");

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.